CMS-2215 Let a Mixin be persisted as an Item
Removed NodeTranslatable since it's no longer needed
Made DataId parseable from String
Added convient method for adding and Iterable of Data to a DataSet
Made Node no longer require name and parent
Added method getNodesByParentPath to NodeJcrDao
..and minor refactorings.

CMS-2221 Create serializer for serializing (and deserialzing) form items to data
Added deserialization